1. Field of the Invention:
The present invention relates to an acrylic fibrous material which permits water to migrate therein as rapidly as required and also relates to a humidity controller provided with said acrylic fibrous material which absorbs water, evaporates water, and controls humidity adequately.
2. Description of the Prior Art:
There is known an open-cell porous sheet made of fine particles of thermoplastic polymer (such as polyethylene, polypropylene, polystyrene, and polymethyl methacrylate) by sinter forming. It finds use as a water vaporizer. However, its usefulness is limited by its insufficient water absorption capacity and rate which result from the hydrophobic nature of the thermoplastic polymer used as the raw material. Attempts have been made to eliminate the hydrophobic nature. For example, Japanese Patent Laid-open No. 860/1991 discloses a composite nonwoven sheet which is formed by laminating a web of short natural fibers or pulp onto at least one side of a sheet of long composite fibers of sheath-core type. Also, Japanese Patent Laid-open No. 86529/1991 discloses a process for producing a composite material. The process consists of bonding fine silica particles (smaller than 1 .mu.m in diameter) to a composite sheet composed of short fibers and a binder resin. The resulting composite material has a porosity of 40-80% and a water absorption rate higher than 30 mm/10 sec. Despite its high initial water absorption rate, its usefulness is limited by its low water absorption at equilibrium.
The above-mentioned prior art technology has a disadvantage of requiring complex steps for combining a hydrophobic substrate with a hydrophilic, water-absorbing material. Moreover, the composite sheet incorporated with natural fibers or pulp as the water-absorbing material is subject to bacterial attack when immersed in water for a long time for use as a humidity controlling sheet or water vaporizing sheet. With bacterial attack, the composite sheet changes in water absorption and permits bacteria to proliferate thereon and to be scattered in the room together with water vapor. This poses a hygienic problem. In the case where hydrophilic fine particles are bonded to a substrate sheet, they also pose a hygienic problem and affect water absorption as they fall off.